1. Field of the Invention
The present invention relates generally to non-destructive test apparatuses that includes a probe for evaluating the intrinsic electromagnetic properties of a dielectric/magnetic structure, and more particularly to an improved open-ended transmission line probe having a conformal tip.
2. Description of the Prior Art
In many scientific and testing endeavors it is valuable to non-destructively test a solid material's electromagnetic properties, such as permittivity ".epsilon." and magnetic permeability ".mu.". A particularly useful apparatus for evaluating the magnetic character of materials is the device disclosed in patent application U.S. Ser. No. 034,344, entitled "Apparatus for Nondestructive Testing of Dielectric/Magnetic Materials" that is assigned to the same assignee of the instant invention, and the disclosure of which is incorporated by reference herein. In a preferred embodiment disclosed in this reference, the apparatus for non-destructive testing of dielectric/magnetic materials includes a probe structure comprising a coaxial cable sensor and a current carrying coil for applying a carefully controlled magnetic field to the solid material being tested. Soft magnetic sleeves surrounding the coaxial cable sensor function to concentrate the applied magnetic field in the specific area of the material to be tested. The coaxial cable sensor functions to transmit an electromagnetic wave into and couple the reflected wave from the sample to a measuring device, such as a network analyzer, so that properties of the material may be quantitatively or qualitatively deduced. Since the surface of solid samples must be flat and polished in order to make accurate and reproducible measurements, these type of sensors have been limited to the laboratory where such stringent conditions could easily be met. In the real world, however, surfaces might not only be rough, but curved.
It is the case that other open-ended coaxial sensors in nondestructive testing (NDT) have been severely limited due to the stringent requirements for the surface finish of the solid materials to be measured. For instance, it is desirable that the coaxial sensor's open end make perfect contact with the surface to ensure that an electromagnetic wave will propagate (fringe) into the material and not be partially reflected due to any air gaps that may be present. Usually this has required that the surface of materials be lapped and polished or that they be soft enough to conform to the probe's open end. This has limited value in the real world where surfaces may not only be rough, but curved.